The invention relates to a valve seat insert cooling system for an air cooled internal combustion engine.
It is known to cool the thermally highly stressed valve seat inserts of exhaust valves of an internal-combustion engine. On the basis of DE-PS 34 12 052, a valve seat insert cooling system is known in which the cooling water used for the cooling of the internal-combustion engine is used as the cooling medium for the valve seats. In this case, the cooling water flows radially into an inlet to the cooling ducts of the valve seat inserts and is discharged through an opening which is opposite the inlet. The outflow openings lead into a duct which leads directly into the intake side of the cooling water pump which supplies the internal-combustion engine with cooling water. This arrangement cannot be used when the internal-combustion engine is air-cooled.
It is known (DE-OS 15 76 727) to cool the valve seat inserts of a liquid-cooled internal-combustion engine independently of the main liquid circulating system by means of another coolant, such as lubricating oil located in a separate coolant circulating system. In this construction, the coolant first flows to the exhaust valve seat inserts and from there to the valve seat inserts of the intake valves.
Here the flow around the seat inserts is not necessarily uniform because of the guiding path of the pipes. In addition, when lubricating oil is used for the cooling of the valve seat inserts, a separate coolant circulating system with a separate pump is required.
It is therefore an object of the invention to provide a cooling system for valve seat inserts of an air-cooled internal-combustion engine. The valve seats are connected to an existing lubricating oil circulating system to achieve optimal and uniform cooling.
According to the invention, this object is achieved by providing a system wherein one feed and one discharge pipe lead into a ring duct in closely adjacent openings. The ring duct has a projection between the two openings which narrows it down considerably. An outlet opening from the discharge pipe is arranged in direct proximity of valve actuation cams in the camshaft housing.
As a result of the manner of feeding and removing the coolant, the whole coolant flow supplied to each valve seat insert flows around the valve seat insert so that the valve seat insert is almost completely encircled by the coolant inflow and outflow. Having the cooling flow directly adjacent the valve seat is of decisive importance for a maximum heat transmission and a uniform cooling. Furthermore, an existing lubricating oil circulating system is advantageously utilized for feeding and removing the coolant lubricating oil. The lubricating oil which is returned from the valve seat inserts, does not flow into the oil sump in an unutilized manner, but rather is sprayed on the cams of the camshaft. This results in a reduction of the wear in the frictional pairing of the cam and its valve and increases the useful life of both parts.
In a first preferred embodiment of the invention, the feed and discharge ducts of the coolant oil can be easily produced as vertical bores (perpendicularly to the joint face between the cylinder head and the camshaft housing).
A second preferred embodiment of the invention requires no boring operation in the cylinder head for the feed and discharge ducts, because they are constructed in one piece with a part of a cooling ring. In this way they are cast into the cylinder head. The cooling ring, surrounding the valve seat insert, is constructed of two cooling ring parts which are welded together with one another. The ring duct extending in the cooling ring is closed off so as to avoid oil leakage. This is particularly advantageous because no oil can reach the combustion space or the outlet duct. In addition, no leakage oil is discharged when the valve seat insert must be exchanged or reworked. The valve seat insert can be exchanged easily and the material for the valve seat insert may be selected arbitrarily and independently of the cooling ring.
In both embodiments, the surface of the ring duct is enlarged by at least two surrounding projections so that an optimal heat transmission takes place.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.